1. Field of the Invention
This invention relates broadly to medical canalicular inserts. More particularly, this invention relates to canalicular plugs which are placed into the punctal opening and vertical punctum to prevent lacrimal fluid from flowing through the lacrimal duct.
2. State of the Art
A variety of eye problems are related to an insufficient volume of tears on the surface of the eyes. The most common is keratoconjunctivitis sicca, also known as dry eyes. Contact lens problems are also often provoked by a lack of tear volume. A common cause for the insufficient tear volume is the drainage of tear fluid through the punctal opening of the nasal lacrimal duct and into the nasal passage, thereby removing the fluid from where it is needed at the eye surface. Furthermore, drainage of tear fluid through the nasal lacrimal duct into the nasal passage is believed to be the cause or associated with several additional problems such as post nasal drip, sinusitis, allergies, headaches, and snoring.
A number of methods for closing the punctal opening have been used to prevent drainage of tears through the nasal lacrimal duct, including suturing, laser sealing, and plugging. Plugging with a canalicular plug such as a punctum plug or a lacrimal plug is the least severe solution, is relatively inexpensive, and is being performed with increasing frequency.
Referring to prior art FIGS. 1 and 2, a punctum plug 10 typically is an elongate member having a relatively large dome-shaped proximal head 12, a relatively large distal body 14 for occluding the lacrimal duct 16, and a relatively narrower cylindrical shaft 18 therebetween. The plug 10 is usually provided with a proximal axial bore 20 for receiving an insertion tool. In addition, the head 12 has a material thickness T.sub.P about the bore 20 which is of sufficient thickness to prevent the head from pushing through the punctal opening 22 and also provides enough mass to permit lifting of the head for removal of the plug without ripping the head. The head 12 is also provided with a peripheral lower surface 21 which is substantially orthogonally oriented to the bore 20 of the plug 10.
Referring to prior art FIGS. 2 and 3, in the punctum plug insertion procedure, the physician positions an insertion tool in the bore 20 of the plug, and, while a physician uses a finger 23 to hold the lower lid 25 open, the body 14 of the plug is directed at the upper or lower punctal opening 22 of the patient. Depending on the anatomy of the patient, the punctal opening 22 is either exposed on the surface 28 of the lid margin 30 or somewhat introverted on the lid margin 30 and lying against the surface of the conjunctiva 32 of the eye. Referring to FIGS. 4A and 4B, the punctal opening 22 has a funnel-like shape which may be substantially circular (FIG. 4A at 22a) or, more commonly, slit-like (FIG. 4B at 22b). When not substantially circular, the opening 22 has a relatively long axis 34 and a relatively short axis 36, with dimensions varying on an individual patient basis (FIG. 5). The long axis 34, where existing, always lies parallel to the posterior lid margin 30 and parallel to the surface of the conjunctiva 32 of the eye.
Referring back to prior art FIG. 2, force is applied to the insertion tool to move the body 14 of the plug 10 through the punctal opening 22 (constricted by the punctal ring 23), the vertical punctum 24, and into the lacrimal duct 16 such that the shaft 18 rests in the vertical punctum 24. The plug 10 is fully inserted when the head 12 seats over and against the punctal opening 22, the shaft 16 rests within the vertical punctum 24, and the body 14 lies within the vertical punctum or other portion of the lacrimal duct 16. Once the plug 10 is fully inserted in the vertical punctum and lacrimal duct, the insertion tool is removed. The punctum plug then operates to block the passage of tear fluid and thereby retain tear fluid at the surface of the eye. Lacrimal plugs which are placed entirely within the lacrimal duct (and below the punctal opening) are also known.
While the use of punctum plugs has generally provoked little patient criticism as to effectiveness and comfort, the most common complaint to physicians relates to the head portion of the punctum plug contacting and irritating the conjunctiva of the eye. There are various reasons why the head contacts the conjunctiva, but most involve individual punctal anatomy and plug size. In particular, the shape of the head and shaft portions of the punctum plug, which have not been substantially changed since U.S. Pat. No. 3,949,750 to Freeman for the original punctum plug device, is believed by the inventor to be the cause, as the dome shaped head and cylindrical shaft do not have satisfactory fit about and within the anatomical structure at the punctal opening and vertical punctum, respectively.